The present invention relates to a method for remotely controlling a video game apparatus with two player systems for two rival players. More particularly, the present invention relates to a method in which the signals transmitted by two transmitters are modulated the same carrier frequency, and the reception of the respective signals from the different transmitters by a receiver need not be synchronous. The received signals, after demodulated and decoded, are identified by the receiver so that the latter can know which of the two transmitters transmits the signals and send the received signals to the corresponding player systems of the video game apparatus.
In a conventional two-channel video game remote controlling system for a video game played by two rival players, like the one shown in FIG. 1, a first and a second infrared transmitter 11 and 15 are provided to send infrared signals respectively to a first and a second receiver 12 and 16 which respectively control a first and a second player system (not shown) in the video game apparatus. The infrared signals are decoded by respective decoders 13 and 17 and sent respectively into the first and second player systems of a video game apparatus. As can be seen in FIG. 2, the first or second transmitter 11 or 15 comprises an input apparatus 21, and encoder 22, a modulator circuit 23, an infrared transmitting circuit 24, an oscillator 25 and a clock generator 26. The encoder receives the data input from the input apparatus 21 which can be a keyboard or a joy-stick, and converts the data into a binary code in form of serial bits (for example, 8 bits). In order to transmit the data, this code is modulated in the modulator circuit 23 by a carrier frequency fc (for example, in the range from 32 KHz to 64 KHz) and transmitted by the infrared transmitting circuit 24.
In conventional method of transmission, for example, pulse frequency modulation (PFM), the different bits 0 and 1 are respectively represented by pulses of different band width. Referring to FIG. 9, in a time duration Tb for transmitting a bit, if there are two narrow pulses, the bit is 1, and if there is only a single broad pulse, the bit is 0. The waveform of the bits 1 and 0 are represented in FIGS. 11 and 12 as an X-stem or an O-stem to facilitate the reading of the contents in the transmission cycle.
All the signals or data to be transmitted (including a starting signal, a system-identifying code, the data from the input apparatus 21, a parity error checking code, and an ending signal) in a transmission cycle Tc are encoded by the encoder 22 and modulated by the modulator circuit 23 into modulated codes. FIG. 11 shows how a bit 0 or 1 is modulated by an oscillating frequency fc. The modulated codes are then transmitted by the infrared transmitting circuit 24 having an infrared LED which blinks in accordance with the modulated codes. Thus the codes are transmitted by the emitted infrared ray from the infrared LED with a carrier frequency fc. [Note: the carrier frequency fc is not the inherent frequency of the infrared rays emitted by the infrared LED of which the spectrum is of the order of GHz, but the "blinking frequency" thereof due to the oscillation frequency fc.]
Referring to FIG. 11, the transmission comprises consecutive transmission cycles Tc, one followed by another without a vacant gap between two adjacent transmission cycles. In other words, the whole transmission cycle is occupied by transmittants (here the term "transmittant" means the all signals or codes to be transmitted, including for example a four-bit starting signal, an eight-bit system-identifying code, an eight-bit data, a one-bit parity error checking code and a-four-bit ending signal. In so far as the player keeps on inputting data, the transmission cycles will be continuously repeated without a pause.
When the transmittants of a transmission cycle Tc is received by a receiver (for example, receiver 12), the receiver 12 will judge if the transmission comes from the first transmitter 11. If this is the case, the transmittant will be received and demodulated. Then from the starting signal, the receiver knows a transmission cycle has begun. From the transmitter-identifying code, the receiver knows whether that the transmission comes from its own system or from an alien system and responsively accepts or rejects it. If the transmission is accepted, the data code will be decoded to make corresponding control of the player system of the video game (for example, upward or downward shift of the cursor). The parity-error-checking code provides an indicator to roughly detect if the received data is distorted. From the starting signal, the receiver knows that the transmission has come to an end, and prepares for the next transmission cycle.
Each of the first and second receivers 12 and 16, shown in FIG. 3, comprises an infrared receiving circuit 31, a band-pass filter 32, an amplifier 33 and a demodulator circuit 34. The transmitted signals from the transmitters 11 and 15, after being received by the infrared receiving circuit 31, are converted into electrical signals, the signal/noise ratio (S/N ratio) of which are raised by the band-pass filter 32. After being amplified by the amplifier 33, the electrical signals are demodulated by the demodulator circuit 34 and sent to the decoders 13 and 17 shown in FIG. 1. To ensure that a receiver (for example, the first receiver) only receives the transmission from one transmitter (here the first transmitter) and not from another transmitter (the second transmitter), the two transmitters must use different carrier frequencies, for the first transmitter, f.sub.c =f.sub.1, and for the second transmitter, f.sub.c =f.sub.2.
Since the carrier frequencies f.sub.1 and f.sub.2 used respectively in the first and the second transmitters 11 and 15 are not of the same value, while the receivers 12 and 16 are respectively tuned to receive only one of the frequencies f.sub.1 and f.sub.2, the first receiver 12 can only receive the signals carried by the first carrier of frequency f.sub.1 and the second receiver 16 can only receive the signals carried by the second carrier of frequency f.sub.2. To ensure the two carriers to be unmistakably identified, their frequencies must not be too close, and also a well-designed band-pass filter 32 is required to prevent the overlap of the received signals with the first or the second carriers of frequencies f.sub.1 or f.sub.2.
For reasons of cost, square wave pulses are utilized in the transmitters, as the aforesaid PFM method suggests. If the square-wave pulses of a transmitter overlap with those of another transmitter, their separation will be difficult and will require a high cost. As stated before, the value of f.sub.1 and f.sub.2 must be as wide apart from each other as possible. Unfortunately, in practical use, they still have to be restricted in a narrow range, namely between 32 KHz and 64 KHz. If the carrier frequency is below 32 KHz, the data rate of the transmission will be too low and the transmission may be easily interfered by a fluorescent lamp of which the pulsation has a dominant spectrum in the range below 32 KHz. When the carrier frequency f.sub.1 or f.sub.2 is in the vicinity of 32 KHz, to avoid the undesired interference, the first and second transmitters must be positioned very close to the receiver. On the other hand, if the transmitted signal has a frequency above 64 KHz, both the transmitting efficiency and the sensitivity of reception are reduced.
Therefore, it is the object of this invention to provide a method for remotely controlling a video game system of a video game apparatus with a first and a second player system corresponding to respective transmitters which modulate and transmit their respective information with the same carrier frequency, for example 50 KHz, which on the one hand, is safely apart away from the 32 KHz lower limit and free from the interference by the pulsation of fluorescent lights, and on the other hand provides a sufficient transmission rate with satisfactory efficiency and sensitivity. In so doing, the necessity of two different carrier frequencies which is responsible for the high cost and low efficiency is eliminated. Moreover, since only a single frequency is needed, it can safely fall in the range of 32 KHz to 64 KHz, without that either the high frequency is above 64 KHz or the low frequency is below 32 KHz.
To use carriers of the same frequency for both transmitters, two problems must be solved:
A. The receiver must be able to identify from which source (the first transmitter or the second transmitter) the information comes, and send it to the correct player system.
B. When information from the first transmitter and that of the second transmitter overlap with each other, if the two transmitters use the same carrier frequency f.sub.3, the separation of the overlapped information will be impossible using conventional method, and a severe interference will occur in both player systems.
The first problem can be easily solved by incorporating a transmitter-identifying code in each transmission cycle transmitted by the two transmitter. Practically, the transmitter-identifying code can be a one-bit code. For example, it can be "0" for the first transmitter and "1" for the second transmitter. From the transmitter-identifying code, "0" or "1", the receiver can identify that the information in a transmission cycle belong to the first transmitter or the second transmitter.
Practically, we can take out one bit from the 8-bit system-identifying code as the transmitter-identifying code, leaving only 7-bits for system identification. (See FIG. 12) For example, the transmitter-identifying bit can be 0 for the first transmitter and 1 for the second transmitter. Thus, in a transmission cycle, the receiver can identify if the transmission comes from its own system by checking the seven-bit system-identifying code, and then identify the source of the transmission (transmitter A or B) by means of the one-bit transmitter-identifying code.
To ensure a transmission cycle of a transmitter (for example A) not to be overlapped, the transmission of another (B) must contain a blank phase in each period which is longer than the duration of a transmission cycle. Since the relative phase position of the transmission of the two transmitters may shift due to their unsynchronousness, the blank phase must be no less than the duration of two transmission cycles to allow a transmission cycle to remain "valid" when shifting within a range of .+-.1/2 T1 (T1 is the duration of a transmission cycle).
Theoretically, a transmission cycle can be immediately followed by another transmission cycle without leaving a gap between them. However, in practical use, a blank gap between the two adjacent transmission cycles is essential to provide an allowance for the probable error in the duration of a transmission cycle. We know that the duration of a transmission cycle may not be always accurately kept at the value T1. It can be occasionally become longer or shorter. If a transmission cycle lasts longer than T1, then its adjacent blank phase will become shorter than it normally would be. As a result, the width of the blank phase may not be broad enough to ensure at least a transmission cycle to safely fall within its span and thus become valid.
Thus a blank gap of duration T2 must be provided as an allowance to offset the likely lengthened transmission cycle.
Therefore, each period of transmission Tp may include a number of intervals T, (T=T1+T2) in which a transmission cycle is present (called "occupied intervals") or absent (called "blank intervals"). The adjacent "blank intervals" (and also the gap adjacent to them) make the necessary blank phase. Referring to FIG. 5, the transmission of transmitter A provides two such "blank phases" of a width=2T+T2, which the transmission of transmitter B provides a single "blank phase" of width=4T+T2. Here each transmission cycle of P.sub.a1 to P.sub.a4 and P.sub.b1 to P.sub.b4 is represented by a rectangle for simplicity reason.
The second problem is solved by "invalidating" (or more correctly "rejecting") all the overlapped transmission cycles and accepting only the unoverlapped ones. In other words, a transmission cycle is taken as invalid and its transmittants rejected by the receiver if its span is overlapped by the span of any transmission cycle of the other transmitter. A transmission cycle is only taken as valid and therefore its transmittants accepted by the receiver when its span is not overlapped by the span of any transmission cycle of the other transmitter. Thus, the interference due to overlapped information of both transmitters is effectively avoid.
The judgment of whether a transmission cycle is overlapped can be easily achieved by conventional technique. Likewise, the rejection of an overlapped transmission cycle and the acceptance of an unoverlapped one can also be accomplished by known means. Thus, the corresponding details are not necessary.
The invalidation of the overlapped transmission cycles must not be such that in a period no valid transmission cycle is left in the transmission of either the first transmitter or the second transmitter. If no valid transmission cycle is left in a period, a transmitter becomes functionless at this moment. Therefore, the distribution of transmission cycles of both transmitters must be such as to ensure that the transmission of any of the two transmitters has at least a valid transmission cycle in a period.
To insure at least a valid transmission cycle in a period, the conventional "time-sharing" cannot be used, since in time-sharing the two transmitters must be synchronized and therefore must be connected on-line with each others. This will make the operation of the remote controllers inconveniently awkward. Thus the distribution of transmission cycles must always ensure a valid transmission cycle in each period regardless of the phase difference of the transmission of the two. U.S. Pat. No. 4,924,216 disclosed a method for controlling a video game for two player systems using a common modulating frequency. To ensure that both player systems have at least one valid transmission cycle within a limited period, each transmission cycle is separated by an equidistant blank phase. Practically, the blank phase must be at least three times that of a transmission cycle for the first player system, and five times that of a transmission cycle for the second player system. Thus, the transmission is sparse and a major portion of the duration of transmission is occupied by blank phase. As a result, the efficiency of transmission is low and the response delay time is considerable.
This invention is directed to providing a more reasonable distribution of transmission cycles which has a high efficiency of transmission and a short delay time.
This invention will be better understood when read in connection with the accompanying drawing, in which: